Using a Proxy server

[bejvn]

I have a Splunk server in a Windows domain that needs to pass a Bluecoat proxy that is in another network to go to the internet.
Authorisation is done by the active directory accounts.

I have checked and tried the recommendations from below articles but still the Splunk server isn't able to connect to splunkbase.splunk.com.

Any suggestion? Does the splunk-launc-conf supports following syntax?
http_proxy = domain\user:password@proxy_serverFQDNS:portnumber

Consulted artciles:
https://answers.splunk.com/answers/93881/splunk-authentication-with-proxy-server.html
https://answers.splunk.com/answers/595/how-to-force-splunk-web-to-use-a-proxy-server-for-external-ca...
https://answers.splunk.com/answers/59873/how-to-get-splunk-to-work-behind-a-proxy.html
https://docs.splunk.com/Documentation/Splunk/7.2.1/Admin/ConfigureSplunkforproxy